California quake on hair-trigger

All of California lives in fear of the next movement of the infamous San Andreas fault. Now seismologists believe that another major earthquake could be triggered by small changes in pressure on the fault.

Chi-yeun Wang, of the University of California, in Berkeley, and Yongen Cai, of Peking University, write in the latest issue of Nature magazine that the fault - responsible for devastating earthquakes in the San Fransisco and Los Angeles areas (right) - is in a critical state.

The two scientists carried out numerical simulations of the seismic cycle in the area, and say that the fault is sensitive to small changes in regional compression.

Increases in pressure may "lock" the fault, they say, making earth movements less likely. But decreases in pressure could release the locked segment, causing ruptures of the fault and sparking earthquakes.

They say that the source of pressure changes could be related to seismic movements in the coastal area.